U.S. patent number 4,155,756 [Application Number 05/860,724] was granted by the patent office on 1979-05-22 for hollow bodies produced by powder extrusion of aluminum-silicon alloys.
This patent grant is currently assigned to Societe de Vente de l'Aluminium Pechiney. Invention is credited to Jean-Louis Mazodier, Rene Perrot.
United States Patent |
4,155,756 |
Perrot , et al. |
May 22, 1979 |
Hollow bodies produced by powder extrusion of aluminum-silicon
alloys
Abstract
This invention concerns production by extrusion of hollow
cylindrical bodies starting with granulated alloys of aluminum
containing silicon. It consists of preparing the composition of the
alloy in a liquid form, producing granules by centrifugal
pulverization or atomization, introducing the granulated material
into an extrusion press to obtain the hollow profile by extrusion
and extruding the granular material within to form a cylindrical
body. This invention is applicable to form hollow bodies and
particularly sleeves of motors of high content silicon aluminum
alloy through which size and distribution of primary silicon is
improved over traditional casting methods.
Inventors: |
Perrot; Rene (Voreppe,
FR), Mazodier; Jean-Louis (Maisons Laffitte,
FR) |
Assignee: |
Societe de Vente de l'Aluminium
Pechiney (Paris, FR)
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Family
ID: |
26219352 |
Appl.
No.: |
05/860,724 |
Filed: |
December 15, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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774424 |
Mar 4, 1977 |
4099314 |
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Foreign Application Priority Data
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Mar 10, 1976 [FR] |
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76 07583 |
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Current U.S.
Class: |
75/231;
123/193.2; 75/236; 75/239; 75/243 |
Current CPC
Class: |
C22C
1/0416 (20130101); F02F 1/20 (20130101); F05C
2203/04 (20130101) |
Current International
Class: |
C22C
1/04 (20060101); F02F 1/18 (20060101); F02F
1/20 (20060101); C22C 001/04 (); F02F 001/00 () |
Field of
Search: |
;75/231,236,243,249
;123/193C,1R |
References Cited
[Referenced By]
U.S. Patent Documents
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1944183 |
January 1934 |
Kempf et al. |
2024767 |
December 1935 |
Jeffries et al. |
3113002 |
December 1963 |
Hollingsworth |
3325279 |
June 1967 |
Lawrence et al. |
|
Foreign Patent Documents
Other References
Dixon, C. F. et al., "Hypereutectic Aluminum-Silicon Alloys
Produced by Powder Metallurgy Techniques", In The International
Journal of Powd. Met., 1(4):28-36, 1965..
|
Primary Examiner: Schafer; Richard E.
Attorney, Agent or Firm: Dennison, Dennison, Meserole &
Pollack
Parent Case Text
This is a division of application Ser. No. 774,424, filed Mar. 4,
1977, now U.S. Pat. No. 4,099,314, July 11, 1978.
Claims
What is claimed is:
1. A hollow body, such as an internal combustion engine sleeve,
produced by powder extrusion of aluminum-silicon alloy with a
silicon content between 15% and 20%, having improved friction and
wear properties and presenting a micrographic structure
characterized by crystals of primary silicon of 2 to 20
micrometers, particles of hardening and anti-friction constituents
selected from the group consisting of silicon carbide, tin and
graphite, fine uniformly distributed pores for promoting
lubrication by providing zones for retaining lubricant, and an
oxygen content between 100 and 15,000 ppm.
2. A hollow body as in claim 1, wherein the aluminum-silicon alloy
contains from 15% to 20% silicon, from 1% to 5% copper, from 0.5%
to 1.5% magnesium, and also from 0.5% to 1.5% nickel.
Description
The invention relates to a method of producing hollow bodies in
aluminum alloys containing silicon and having improved properties,
particularly as regards friction properties, compared with hollow
bodies produced from these alloys by prior-art methods. These
hollow bodies are for example sleeves of internal combustion engine
cylinders, the bodies of hydraulic jacks and, in a general way, any
hollow product that has a constant or only slightly variable
cross-section over its entire length and that requires good sliding
properties.
Such hollow bodies are usually produced by either of two
techniques, namely:
A CASTING TECHNIQUE: THIS METHOD IS USED FOR PRODUCING CAST-IRON
AUTOMOBILE ENGINE SLEEVES, GENERALLY BY CENTRIFUGAL CASTING, AND
ALUMINUM ALLOY ENGINE SLEEVES BY PRESSURE-CASTING;
AN EXTRUSION TECHNIQUE: THIS METHOD IS SOMETIMES USED FOR PRODUCING
THE SEMI-FINISHED PRODUCTS FROM WHICH ALUMINUM ALLOY PUMP BODIES
ARE MADE, THE IMPACT-EXTRUSION OF CAST OR CUT DISCS BEING USED.
When aluminum alloys are used for producing these hollow bodies
and, more particularly when the products are the sleeves of
internal combustion engines, the present tendency is to make use of
alloys containing silicon, and, particularly, hypereutectic alloys,
i.e. alloys having a silicon content averaging above 12%. This type
of alloy is particularly suitable for these uses for two main
reasons, namely:
(1) The hypereutectic Al-Si alloys have a lower coefficient of
expansion than the other aluminum alloys, and this is clearly of
advantage when the parts in question move relatively to each other
with a small controlled clearance between them, and when they
develop heat during operation.
(2) The presence of hard primary Si crystals in a softer aluminum
matrix makes these alloys particularly suitable, with or even
without subsequent surface treatment, for providing surfaces having
micro-rugosities which favor the retention of lubricants.
However, this eutectic composition is not precisely defined and,
because of divergences from equilibrium, crystals of primary
silicon always occur in alloys that are very close to being
eutectic, such as A-S13 or A-S12 UN, and even in alloys of
hypoeutectic composition such as A-S10 UG.
A great difficulty in the manufacture of these parts in alloys
containing very large amounts of silicon or having a hypoeutectic
structure consists in the fact that the crystals of primary Si
should not be too large. The acceptable maximum size is generally
100 micrometers. However, this requirement is difficult to meet in
castings, particularly if they are of fairly large dimensions.
Also, the silicon crystals in extruded parts are only slightly
broken up as compared with the initial cast billet, and the same
difficulties still occur.
The applicants have invented a process for preparation of hollow
bodies of aluminum alloys containing primary silicon and
particularly containing from 12% to 30% silicon and preferably from
15% to 20%, and also from 1% to 5% copper, from 0.5% to 1.5%
magnesium, and from 0.5% to 1.5% nickel.
These hollow bodies have the following properties:
the primary silicon is of a size less than 20 microns, whereas the
previously used methods have led to these crystals having a size
greater than 20 microns;
their porosity is low and is not concentrated in certain zones
which could be the cause of mechanical weakness or lack of
tightness with respect to fluids under pressure such as is
sometimes the case with pressure-cast products;
their ductility is better than that of the conventional cast
product;
they have better friction properties than those of the prior art
products;
their performance as regards friction can be further improved in
comparison with those of the products hitherto used for these
purposes, by incorporating in the alloy compounds which promote
resistance to wear or reduce the coefficient of friction; and
they can be machined much more easily than the products of similar
composition produced by the conventional methods.
IN THE DRAWINGS
FIG. 1 shows, at a magnification of 200, a micrograph of a sample
taken from a hollow body in an alloy of the A-S17 U4G type
(containing approximately 17% of silicon, 4% of copper and 0.5% of
magnesium), obtained by powder extrusion. Most of the silicon
crystals (in black) have dimensions less than 20 .mu.m.
FIG. 2 shows, at the same magnification of 200, a micrograph of a
sample taken from a hollow body made of the same alloy but obtained
by low-pressure casting. The difference in the size of the crystals
can be clearly seen.
FIG. 3 shows, in elevation and side view, slide test pieces in the
form of two tangent discs.
The method of the invention consists in using granules of aluminum
alloy obtained by pulverization, in extruding these granules to
form hollow bodies and, finally, in machining the hollow bodies
thus obtained. The complete system for producing these hollow
bodies is therefore as follows:
preparation of ingots of an alloy, for example an alloy of aluminum
base containing between 15% and 20% silicon, between 1% and 5%
copper, between 0.5% and 1.5% magnesium, and also 0.5% and 1.5%
nickel.
remelting of the ingots and granulation of the molten metal thus
obtained by any of the existing processes, for example, centrifugal
pulverization, atomization or the rotating electrode method; the
particle-size of the product thus produced being between 5.mu.m and
2 mm. Depending upon the method of preparation used, the
particle-size will vary as will the cooling rate of the particles,
resulting in a varying size of the silicon particles. Thus, in the
case of granules produced by centrifugal pulverization and having a
particle-size of between 300 .mu.m and 2 mm, the size of the
primary silicon particles will be between 2 .mu.m and 20 .mu.m,
whereas for particles formed by atomization and having a size less
than 100 .mu.m, the size of the primary silicon particles will be
less than 5 .mu.m;
optional mixing of the granulated alloy material thus obtained with
granules of silicon carbide, tin or graphite;
optional isostatic or mechanical compression of the granules;
optional heating to extrusion temperature of the granules which may
have been previously compressed;
introduction of the granular material, compressed or otherwise,
into the container of the extrusion press;
extrusion of tubing forming the sleeves; this is a conventional
extrusion operation for producing hollow bodies and can be carried
out using either of the two usual methods well known to the expert
in the field:
bridge extrusion; the bridge, located upstream of the die in the
path of movement of the metal, secures a mandrel within the die so
that the bore of the tube is formed;
extrusion with a plain die and a floating mandrel which advances
with the extrusion pad; (it is then necessary to use a hollow slug
of compressed granular material which has an axial hole formed
therein in which the mandrel is accommodated during extrusion);
optional dressing and sizing;
optional stabilization heat-treatment; and
removal of material from inside the tubes, and machining.
It is important to point out that certain of the succession steps
constituting the above-described system are optional:
the mixing of the granulated alloy material with granules of
silicon carbide, tin or graphite is for the purpose of imparting to
the hollow bodies, subsequently formed by extrusion, special
degrees of hardness (silicon carbide) or good sliding properties
(tin or graphite);
the precompression of the granular material is not essential
either. This precompression may be carried out either cold or hot
with the possible use of varying negative pressure so as to
facilitate the suppression of porosity in the extruded product.
The hollow bodies produced in accordance with the above-described
method have a certain number of notable properties. First, their
friction characteristics are distinctly improved, compared with
those of the known products. In the examples detailed below for
illustrating the invention, the experimental method whereby this
improvement can be shown is indicated.
This improvement involves obtaining a particularly fine product
structure. The size of the crystals of primary silicon is less than
20 microns and, by selecting the appropriate production method, can
be kept below 5 microns. With conventional casting methods, such as
pressure casting or low-pressure casting, the size varies between
20 and 80 microns.
In FIG. 1, the micrograph is of a sample from a hollow body in an
alloy of the A-S17U4G type (containing approximately 17% of
silicon, 4% of copper and 0.5% of magnesium), obtained by powder
extrusion. Most of the silicon crystals (in black) have dimensions
less than 20 .mu.m.
In FIG. 2, the micrograph is of a sample taken from a hollow body
made of the same alloy but obtained by low-pressure casting. The
difference in the size of the crystals can be clearly seen.
The improvement also involves the presence of fine, uniformly
distributed pores promoting lubrication by creating zones to retain
oil. In cast products the pores are distributed unevenly and may
occur in very great numbers in localized zones.
The improvement further involves the possible presence in the
matrix of compounds such as silicon carbide, tin or graphite which
improve resistance to wear or reduce the coefficient of
friction.
Secondly, parts obtained by the method of the invention have a
remarkable wear behavior distinctly better than that of alloys of
similar composition worked by conventional methods. This behavior
is revealed in excellent chip formation, good surface and in
particular, light tool-wear. This good behavior results from the
absence of crystals of primary silicon of large size, the effect of
which is vary damaging in machining operations.
In the third place, the product obtained has fine, well distributed
pores. Thus, there are no areas of reduced mechanical strength or
areas which can be penetrated by fluids under pressure such as
occur in pressure-cast products.
On the other hand, this product has distinctly greater plastic
range, i.e. difference between tensile strength and yield strength,
of 15 hbars and elongation of 5%, than that of cast products
wherein elasticity is virtually non-existent as indicated by the
elastic limit (in the order of 0.5 hbar) and elongations of less
than 1%.
To summarize, the hollow bodies made by powder-extrusion are
notable, from the metallurgical point of view, because of the size
of the crystals of primary Si being less than 20 .mu.m, small,
evenly distributed pores and the alignment of constituents that is
characteristic of the special texture of all extruded products.
Furthermore, their oxygen content, resulting from the surface
oxidation of the granulated material, is between 100 ppm and 15000
ppm.
Also, the method of the invention has a number of features which
enable the production procedure and the finishing operations on
these hollow bodies to be considerably simplified. The provision,
by extrusion, of a product having dimensions very close to the
final dimensions and possessing a good surface condition is a
considerable advantage over the casting methods which call for
considerable machining to bring the product to the required
dimensions and surface condition; the greater ease in machining the
powder-extruded products, as compared with products obtained by
impact-extrusion or pressure casting, enables machining to be
carried out more economically and tool-wear to be reduced; and the
use of either alloys having a composition and structure not
obtainable by existing methods, or composite products consisting of
the basic alloy and additions, such as silicon carbide, tin and
graphite, makes it possible, in most cases where the products are
used as sliding parts, to dispense with the surface treatments that
have sometimes been necessary in the past.
In certain cases however, it will be advantageous to carry out a
chemical treatment of the surface following a polishing or grinding
operation. The object of this treatment is to smooth out the
crystals of primary silicon over which a part will rub when moving
relatively to the hollow body.
The following Examples serve to illustrate the invention and to
make it more readily understood.
EXAMPLE I
Internal combustion engine sleeves were produced by the following
succession of operations:
(a) Preparation of an A-S17U4G alloy having the composition:
______________________________________ Si = 16.80% Cu = 4.40% Mg =
0.55% Fe = 0.80% Al = remainder
______________________________________
and refining of the primary Si by the addition of phosphorous in
accordance with a known technique.
(b) Production of the granulated material.
The cast metal was brought to a temperature of approximately
850.degree. C.; it was held at this temperature for 30 minutes and
then pulverized by centrifuging. The size of the particles thus
obtained was between 50 .mu.m and 2 mm. The structure of the
particles thus obtained was fine; the crystals of primary silicon
were of a size varying between 2 .mu.m and 20 .mu.m maximum.
(c) Powder-extrusion of tubes to be used as sleeves; this operation
was carried out in the following manner:
The extrusion press was a conventional press equipped with bridge
tools. Without having been heated or precompressed, the granulated
material was introduced into the container of the extrusion press
in a loose mass; the container and the tools were not lubricated
but were heated to a temperature of approximately 450.degree. C.;
to prevent the granulated material from flowing through the die
during charging of the container, an aluminum foil was placed in
front of the die. The extrusion pad was then fitted at the inlet to
the container; the ram was applied so as to compact the granulated
material; the pressure applied to the ram was increased until it
was sufficient to cause the metal to flow through the die after the
granulated material had been completely compacted. This metal-flow
sufficed to ensure compactness in the extruded product and cohesion
between the particles of the initial material; this flow in fact
enables the oxide layer on the surface of the particles to be
broken and thus creates metallic surfaces, completely free from
oxide, that could readily fuse together when brought into contact
with each other.
(d) Dressing of the tube by a conventional drawing operation.
(e) Cutting of the tube into lengths corresponding to those of the
sleeves.
(f) Stabilization heat-treatment for several hours at a temperature
of 220.degree. - 250.degree. C. (this temperature being higher than
that to which the products are subjected when in use).
(g) Machining of the sleeves to the final dimensions.
The sleeves thus obtained had a very fine metallurgical structure
similar to that illustrated in FIG. 1.
The mechanical properties were measured by means of tensile tests
carried out on test-pieces cut in the direction of extrusion (L)
and in the direction transverse thereto (T). For comparison
purposes, the mechanical properties of the same alloy,
pressure-cast, and of cast-iron are given:
______________________________________ B.L. El. % Direction hbars
5.65 .sqroot.SO ______________________________________ A-S17U4G L
26.6 5.0 powder-extruded T 25.2 3.7 A-S17U4G pressure-cast 29.0
<1.0 Cast-iron 20 to 40 <1.0
______________________________________ B.L. = breaking load (in
hectobars) El. = elongation measured on the basis of 5.65
.sqroot.So So = cross-section of test-piece
It was observed that with a breaking load approximating very
closely to that of A-S17U4G, pressure-cast, and of cast-iron, the
elongation values recorded for extruded A-S17U4G are higher, which
indicates a much reduced brittleness.
Sliding behavior was determined by a simulation test carried out in
the following manner. The slide test-piece took the form of two
tangent discs as shown in FIG. 3 (shown in elevation on the right
and in side-view on the left). The discs were caused to rotate so
as to cause a 10% pure slip (in angular speed) between the two
test-pieces in contact; oil at a constant pressure was introduced
at the zone of contact, and during the test the following could be
measured; the load P applied to the upper disc,
the contact temperature, and
the frictional torque.
The test-pieces were annular discs, having a thickness of 10 mm and
an inside diameter of 16 mm.
The lower disc, in A-S12UN had an outside diameter of 65 mm and was
used as a reference (numeral 1 in the drawing).
The other disc was made of the test metal and had an outside
diameter of 35 mm (numeral 2 in the drawing).
The sliding tests were carried out in two stages; first stage,
seizing test; second stage, wear test. Each of these two tests
started with a running-in period.
Seizing Test
After a running-in period during which the two samples were placed
in contact with each other under a relatively low load and in which
the discs were rotated at constant speed, this test consisted in
periodically increasing the load until seizing occurred, this
mainly manifesting itself during the test by a sudden increase in
the contact temperature, and by an increase and, in particular,
destabilization of the coefficient of friction. The load being
applied at the moment when seizing occurred was called the
"gripping load".
Wear Test
This test, was preceded by a running-in operation identical to that
used in the seizing test, and it consisted in carrying out a
sliding test using a constant load equal to 0.5 to 0.8 times the
seizing load and applied for a period of 2 to 5 hours, and in
measuring the loss in weight of the test-pieces during the course
of the test.
The results of these sliding tests as shown in the following table
wherein the values recorded for the powder-extruded alloy, the
pressure-cast alloy, the alloy cast under low pressure and
cast-iron are compared:
______________________________________ wear in mg Seizing
Coefficient Disc in Disc in load of friction A- A-S17U4G or daN at
P = daN S12UN cast-iron ______________________________________
A-S17U4G powder-extruded 90 0.015 67 8 A-S17U4G pressure-cast 80
0.015 52 12 A-S17U4G cast under low- 30 0.045 -- -- pressure
cast-iron 80 0.109 2 100 0.5
______________________________________
This test showed that the behavior of powder-extruded A-S17U4G is
comparable with that of the pressure-cast alloy A-S17U4G as regards
the seizing loads, the coefficient of friction and the wear on the
parts. On the other hand, the behavior of the product produced by
powder-extrusion is markedly superior to that of the same alloy,
cast under low pressure, which has an appreciably lower seizing
load and a higher coefficient of friction than in the two other
cases. The behavior is also considerably better than that of
cast-iron which, for an identical seizing load, has a higher
coefficient of friction and as regards which the wear of the
contacting part in aluminum alloy occurs more rapidly.
EXAMPLE II
(a) Preparation of an A-S25U4G alloy having the composition:
______________________________________ Si = 25% Cu = 4.3% Mg = .65%
Fe = 0.8% Al = remainder ______________________________________
and refining of the primary Si by addition of phosphorous in
accordance with a known technique.
(b) Production of the granulated material.
The cast metal was raised to a temperature of approximately
900.degree. C. and was held at this temperature for 30 minutes and
then pulverized by atomization. The size of the particles thus
obtained was between 5 .mu.m and 500 .mu.m. Only those particles
having a size of less than 100 .mu.m were retained. The structure
of the particles thus produced was fine; the crystals of primary
silicon had a size of less than 5 .mu.m.
(c) Cold compacting.
The granulated material was compacted cold in a vertical press and
under a pressure of 50 kg/mm.sup.2.
(d) Extrusion of tubes for use as sleeves.
This operation was carried out on a conventional press provided
with bridge-type tools. The compacted slug was extruded without
heating, as a conventional solid billet.
(e) Dressing of the tube.
This was done by a conventional drawing operation.
(f) Cutting of the tube into lengths corresponding to the length of
the sleeves.
(g) Stabilization heat-treatment for several hours at 220.degree.
C.- 250.degree. C. (which temperature is higher than that at which
the sleeves are used), or solution heat-treatment, quenching and
tempering.
(h) Machining of the sleeves to the final dimensions.
The metallurgical structure of the sleeves thus obtained was very
fine, and the size of the silicon crystals was less than 5 .mu.m.
It was also observed, after heat-treatment, that the pores were
very fine and evenly distributed in the product.
The mechanical properties, measured in the same way as in the
previous Example, are shown in the following table:
Sleeves in A-S25U4G produced by powder-extrusion:
______________________________________ B.L. El. % Direction hbars
5.5 .sqroot.So ______________________________________ L 29 4
Stabilized T 28 2.5 In solution L 55 2 quenched and tempered T 52
0.7 ______________________________________
It will be seen that the material exhibits high breaking loads
associated with quite considerable elongations.
Regarding the sliding properties, the same simulation tests were
carried out as in Example I.
The performances of this alloy were identical to those of A-S17U4G,
shaped by powder-extrusion of low-pressure casting, as regards the
seizing load and the coefficient of friction; on the other hand,
wear resistance is appreciably increased; loss in weight per unit
of time is reduced in a ratio of 1.5 to 1.0.
* * * * *